As shown in FIGS. 1 and 2, Long bones of children like femur (1) and tibia (2) are having growing ends—epiphysis (3) having growth plate (4), a nongrowing shaft—diaphysis (5) and intermediate part—metaphysis (6). Injury or irritation to this epiphysis (3) directly or indirectly hampering its blood supply leads to deformity of bone and limb. Treatment of Fractures of long bones of weight bearing lower limb like femur (1)—thigh bone, tibia (2) and fibula—leg bones and non weight bearing upper limb bones like humerus (54)—arm bone, radius (55) and ulna (56)—forearm bones, particularly fractures of shaft or diaphysis (5) many a times require its fixation with nails. To prevent injury to epiphysis (3), entry of such nails required away from the ends of long bone from sides and angled. For such side-angled entry of nails in long bones, require very high flexibility and strength from material of nail. Flexibility of nail is measured indirectly by its ductility, which in turn measured as percentage of elongation of nail during testing of nail on universal testing machine. Strength of nail is measured as stress applied on nail in units of Mega Pascal (MPa) on universal testing machine. Flexibility of nail helps surgeon to have different curves at desired distance and angle to facilitate its introduction in medullary canal (7) and gives multiple point contact to maintain fracture fragments in correct relation during knitting. Long bones of children are elastic and are having different curvatures. Long bones of children are growing, so it requires removal of nails earliest after solid union of fracture.
Experiences of surgeons and clinical studies and mechanical studies have shown that treatment of fractures of long bones by flexible nails require implant assembly with proper biomechanical properties, such as:                It requires high flexibility at the same time high strength to get more curvatures and multiple contact points at medullary canal and due to high flexibility; it should not require two opposite entry sites to balance opposing force of curvatures.        It requires pathfinder-gliding tip to glide in medullary canal, not injuring epiphysis or perforating opposite cortex while making entry in medullary canal.        It should be of universal length to have latitude to surgeon to select any fraction of length suitable for better fixation, at the same time avoid penetration of proximal epiphysis, and avoid irritation of soft tissue at distal end of nail.        It should have facility for surgeon to choose different cross section diameters in combination to get adapted well in any size of medullary canal.        It should have a non leading or projecting end such that it does not irritate soft tissues around it at the same time provide means for easy removal after solid union of fracture without much difficulty.        By having multiple curves and multiple contact interference fit, by rotation of nail it should allow rotational or lateral movement of fracture fragments to improve relation and contact between fragments.        It should allow limited axial loading of fracture fragments without displacement on weight bearing by patient to stimulate bone healing.        It should not back out at knee or non-leading end or penetrate joint on weight bearing by patient.        It should be minimally invasive to patient.        
Along with these biomechanical properties, the implant unit should be easy to fix and should provide maximum accuracy of fixation. Therefore, it is adoptable to average surgeon giving reproducible results. It should be cost effective too.
Nails and other devices placed in medulary canal for fractured long bone are in use since long.
Rush, U.S. Pat. No. 2,579,968, Dec. 25, 1951, as shown in FIG. 3A, 3B, discloses a pin (8) of flexible resilient material like stainless steel and which is originally straight except for a slight curve or bend at its forward sharpened end (9). The particular feature taught by the patent resides in the shape of the sharpened distal end, by which that end, in penetrating the medullary canal, is cammed free of the cortex during movement there along. Here, flexibility is less, sharp end does not glide easily in medullary canal, and penetration of opposite cortex of bone is known to occur. Length of pin (8) is not universal. Hooked end (10) can cause irritation.
Herzog U.S. Pat. No. 2,998,007 Aug. 29, 1961, teaches a stiff rigid steel tube open at both ends and pre-shaped if required by the contour of the particular bone to be repaired. The tube has longitudinal slot at spaced locations along its length. Once emplaced, through an incision at the proximal end of the bone, spring wires are pushed into and through the tube and manipulated so that their ends project from appropriate ones of the slots to become anchored in the cancellous. Thus, the patented device is relatively complicated, difficult to install and properly manipulate. Apparently, it immobilizes the patient's joint at the proximal end of the bone.
Another prior art device is shown by Fischer et al., U.S. Pat. No. 3,779,239, Dec. 18, 1973, showing a complicated structure including a rigid tube or sleeve pre-shaped to conform to the normal shape of that particular bone. At its distal end, the tube carries an expansible section. When the tube and its expansion section are driven into the bone canal through an incision at the proximal end thereof, a rod in inserted into and along the tube, then threadedly attached to the terminal expansion section. Turning of the rod further then causes the expansion of the section to anchor the device within the bone. The device thus shown is complicated and expensive. During emplacement lateral thrust engendered by turning of the flexed rod, tends to cause undesirable transverse movement of the fractured parts due to tendency of the tube to shift or turn in and with respect to the medullary canal. The expense and difficulty in storage of the large number of such devices necessary to service any fractured bone of the body, are clear.
Ender et al., U.S. Pat. No. 4,169,470, Oct. 2, 1979, as shown in FIG. 3C, 3D, discloses thin, flexible, elastic, resilient Ender nails (11) pre-shaped for an adult femur curvatures, fixed length from 32 to 49 cm, preferably of diameter of 4.5 mm, having pointed proximal end (12) and flat eye shape (13) at distal end. It is made of metal having elasticity between about 125 Kp/mm.sup.2 to 145 Kp/mm.sup.2 (claim no. 21).
After fixation, it gives three point fixations due to its curvatures (14). After final fixation, with multiple Ender nails (11) at the distal end being flat to permit a fish-scale type-mating overlying with the distal ends of a plurality of other similarly shaped nails when protruding in situ through the incision in the bone. One of the disadvantages is the flattening at the distal end, which are oriented transversely to the axis of curvature. These nails are in addition provided with an aperture for the purpose of obtaining an effective engagement of a drive-in tool, may be effective in the manner of a chisel if they do not come to lie completely flat against the bone and in parallel therewith, respectively. The relatively sharp edges formed in this manner may have an irritating effect on the adjacent tissue. As the flattening is normally formed in an upsetting process, additional processing is required so as to remove any burrs or sharp edges formed in said upsetting step. Through the flattening of a round nail cross sectional area, in addition, a critical zone of transition (15) will form having a relatively high notch effect, so that with a considerable amount of torque applied at the distal end (13) a plastic deformation or even a shearing off may be the result in this zone. Upon rotation of the distal ends (13) against each other, several flattened distal ends require a relatively great amount of space, whereby the well-being of the patient may be affected. Problems with this nails are it is stiffer for use in pediatric long bones, not having enough flexibility leading to straightening of curvatures of bones, pointed end (12) many a times penetrates super-adjacent fracture fragment and penetrate in hip joint (21), which is considered to be a serious complication of the method of treatment rendering it ineffective. On axial loading by weight bearing on limb, due to insufficient ductility or flexibility, it backs out at distal end thereby increases tissue irritation already present at protruding distal end. Other disadvantages are its pre-shaped curvatures not suitable for long bones of children and lesser diameter than 3 mm is routinely required for narrow medullary canals of long bones of children and in certain occasions in adults having poliomyelitis or narrow medullary canal due to other reasons.
Kalmert. U.S. Pat. No. 4,473,069, Sep. 25, 1984, showing similar nails as Ender's nail (11), but it is having a means for prevention of back out of nail, having a separate element, a coupling piece with a plate portion which can be mounted to the outside of the bone by means of one or more cross screws. A coupling hook projects from the plate portion, which forms a cross head and can be brought to engage lockingly the elastic nail by the cross head being passed through a slot in one end of the nail and being rotated. Other disadvantages are same as Ender's patent.
Harder et al. (U.S. Pat. No. 4,712,541, Dec. 15, 187) showing improvisation of Ender's nail (11) by providing a distal end without eye and a proximal end or tip of nail as a rounded-off thickened portion in place of a sharp slanted tip. Other disadvantages are same as Ender's patent.
Walker, U.S. Pat. No. 4,457,301, Jul. 3, 1987, shows an intramedullary bone fracture fixation device comprising a plurality of thin resilient pins substantially longer than the fracture zone to be fixed and a flexible core element holding the pins apart from one another in a desired special arrangement over substantially the full length of the pins. This device with said pins being held in sliding fit in longitudinal grooves in the periphery of said flexible core, wherein the pins are made of titanium alloy Ti-6Al-4V, and the core is made of ultra-high molecular weight polyethylene. Wear of plastic will cause osteolysis. It does not provide any firm anchorage to proximal ends of pins. Due to titanium alloy and ultrahigh molecular weight polyethylene cost of device becomes very high, not affordable to all patients.
Hinze PCT/EP98/01018, Publication No. WO 98/36699, Aug. 27, 1998 shows a fracture nail made of a nickel-titanium alloy which is plastically deformable at a temperature lower than the human body temperature and which returns to its original shape at the body temperature. At the body temperature, the fracture nail has at least one deviation from its straight central axis and at a lower temperature; it can be brought to a substantially straight shape. The fracture nail can thus be firmly braced within the medullary cavity and fully stabilizes the bone. Disadvantages with this nail are it has thermal mechanical-shape memory at particular temperature only, which is difficult to maintain many times during surgery, it has no latitude to surgeon to give desired curvature according to site of fracture. Practically to use this nail is very difficult and due to use of shape memory alloy, cost is high. The ends of nail are sharp pointed. Other examples of use of shape memory alloy are Levy, U.S. Pat. No. 6,783,530, Aug. 31, 2004 and Cheung et al., U.S. Pat. No. 20040230193, Nov. 18, 2004.
Burkinshaw et al., U.S. Pat. No. 6,551,321, Apr. 22, 2003 shows an orthopedic implant including a pair of spaced apart end caps, which are interconnected by a plurality of elongated flexible members. Each end cap includes an aperture formed there through for the use of a trochanteric guide wire for piloting the implant during trial insertion and final insertion into an intramedullary canal. At least one of the end caps includes a rounded end to enhance insertion. Preferably, the flexible members are bowed outwardly to provide a “birdcage” configuration. Disadvantage of this nail is, it is having rigid part at both end secured with flexible part, having flexibility in particular part only, thus not allowing entry point of nail at side and angled to side of long bones of children to prevent injury to epiphysis. It is not having universal length, so requires large inventory of different length and different diameter combination.
Presently used Titanium Elastic Nails (TENs) (16) marketed by Synthes (Paoli, Pa., U.S.A.) are elastic nails made of titanium alloy and recommended for use in fractures of long bones of children. These nails are available in different diameter from 2.5 mm to 4.5 mm, having universal length of 45 cm. As shown in FIG. 3E, it is having a leading or proximal end (17) made flat and bent like hockey stick for entry into medullary canal (7). Distal end (18) is rounded. Through the flattening of a round nail cross sectional area, in addition, a critical zone of transition (15) will form having a relatively high notch effect, so that with a considerable amount of torque applied at the distal end (18), a plastic deformation or even a shearing off may be the result in this zone. Other disadvantages are it is made of soft material of titanium alloy having been reported breakage of nail on repeated bending and straightening while insertion or removal. It is reported in study (J. M. Flynn et al., Journal of Pediatric Orthopedics, Vol. 21, No. 1, 2001 Page, 4-8) that TEN (16) technique requires balancing the forces of the two opposing flexible nails. For the same it requires contour of the nails with an identical gentle curvature, and have to use two different, medial and lateral starting or entry points that are at the same level in the metaphysis (6). It is further reported that to balance it requires same diameter opposing flexible nails to prevent mal-relation of fracture fragments like varus and valgus. It is also reported that for easy removal of nails when required, it is recommended to bend a little distal end to facilitate the application of removal device later on. This bent extra osseous part causes local tissue irritation and pain. Proximal end having flat hockey stick shape (17) bend can cause difficulty in smooth gliding of nail in medullary canal (7) and surgeon has no intraoperative latitude to change the angle of bend according to angle of entry point. Tested on universal testing machine, 3 mm Titanium Elastic Nail (16) shows percentage of elongation only 8% on tensile stress applied, which is the indirect evidence of ductility or elasticity. Test also shows Ultimate Tensile Strength of 1211.14 MPa. Problem of requirement of balancing force of two opposing nails of same diameter having identical curvature with same level two different entry points to prevent mal-relation of fracture fragments is probably due to low flexibility of nails. This nail is made of titanium alloy, which makes its cost high.
Mechanical and clinical studies undertaken by inventor have revealed technical problems and disadvantages with prior art.